1. Field of the Invention
The present invention relates generally to devices for removing obstructing material from body passages and, more particularly, to an access device configurable between a first small diameter for initial insertion into a body passage and a second larger diameter for effecting the removal of obstructing material.
2. Discussion of the Prior Art
The prior art includes many devices for removing obstructing material from body passages. When the body passage comprises a blood vessel, obstructing materials may include plaque, thrombus, embolus, clots, and fatty deposits. In other cases, obstructions may result from stones and strictures.
Catheters are commonly inserted into vessels for the purpose of dislodging obstructing materials from the vessel walls. In a prevalent technique commonly referred to as an embolectomy/thrombectomy procedure, a balloon tipped catheter is introduced through a surgical incision and into a blood vessel. The balloon tipped catheter is advanced to the location of the obstructing material or occlusion, and the balloon is then inflated at a point within the vessel beyond the point of the obstructing material. The catheter including the attached balloon is then pulled back to the point of insertion. In this manner, the balloon pushes the obstructing material to the point of insertion where it is removed through the incision. When the obstructing material is detached from a vessel wall using this technique, the obstructing material will often have a tendency to disperse and migrate with the flow of blood within the vessel. This dispersion can make collection and removal of the obstructing material difficult, and the migration can put the patient at risk of acute trauma. Thus, a problem associated with this embolectomy technique involves the efficient collection and removal of obstructing material while preventing migration and dispersion of the obstructing material. Other percutaneous procedures exist in the prior art for recanalization of vessels. One percutaneous procedure involves the use of laser energy to vaporize the stenotic material. Another percutaneous procedure, commonly referred to as aspiration embolectomy/thrombectomy, relies on a negative pressure to collect the obstructing material.
Percutaneous or minimally invasive access to a blood vessel in the case of a balloon catheter, for example, requires the catheter to have a very small diameter to fit through a corresponding small incision in the blood vessel. Once the catheter is in the blood vessel, however, portions of the catheter need to assume a large profile removal interface for efficient removal of the obstructing material from the lumen of the blood vessel.
In an attempt to meet this dual functional requirement of small incision diameter and large intraluminal operating diameter, the prior art has incorporated sheaths in conjunction with catheters. U.S. Pat. No. 5,011,488 to Ginsburg discloses the use of an expanding funnel-shaped sheath for use in withdrawing thrombus or embolus (obstructing material) from a blood vessel. The funnel is deployed by extending the expanding funnel-shaped sheath from within a second sheath to thereby allow the compressed funnel to expand radially. Use of this second sheath tends to increase the overall diameter of the device, thus increasing the size of the incision required for insertion of the device. In addition to not achieving an optimally small insertion diameter, this device is also unable to obtain an optimally large intraluminal operating diameter. An optimally large intraluminal operating diameter would allow for better insertion and removal of larger instruments through the sheath. This prior art technique of inserting both the introducer sheath and the pre-shaped funnel sheath into the body passage, and of subsequently removing the introducer sheath, requires the large introduction incision to form a seal around the smaller diameter pre-shaped funnel sheath after the introducer sheath is removed. In other words, the double sheath combination of the prior art requires an initial incision into the body passage large enough to accommodate the introducer sheath and, subsequently, small enough to adequately form a seal around the smaller pre-formed funnel sheath left in place after the introducer sheath is removed. Since the initial incision cannot be subsequently reduced in size to accommodate the funnel sheath, a good seal in this prior art system is difficult to obtain.
Other devices, which provide access to relatively inaccessible regions of blood vessels, are disclosed in U.S. Pat. No. 4,530,698 and U.S. Pat. No. 4,437,859. Needle and sheath combinations for use in drug delivery, blood withdrawal, and dialysis have been proposed by the prior art, but these devices incorporate different structure to solve a problem, which is different than the removal of obstructing material from a body passage. U.S. Pat. No. 5,234,425 to Fogarty discloses a variable diameter sheath constructed of a composite elastomeric material that may be stretched to reduce the diameter. This variable diameter sheath, however, is not used for the removal of obstructing material. Instead, the primary goal of this device is to provide a lining of a body passage with a thin walled single thickness interior sheath, which is introduced into the body passage in a reduced diameter condition and subsequently expanded to snugly fit the interior wall of the body passage. The variable diameter sheath incorporates a tubular braid encapsulated within a coating of high elongation silicone polymer. None of the prior art devices disclose a sheath, which is efficiently configurable between a minimum diameter and a maximum diameter, and which comprises a lumen for accommodating a catheter to facilitate removal of obstructing material from a body passage.